Script function changes!

i have [login to view URL] script and i want to add a few extra function on it... i want to turn it vendor shop where user can sell their [login to view URL] ones product purchased by buyer,the payment will not go direct seller account which will go admin account! lets say kind of escrow [login to view URL] the buyer happy with item,he will mark the deliver item as complated then only money will go user account by admin approve... if the buyer did not like the item an want revision,on the purchase deteail page,will ask revision,this revision will be set by admin! lets say 5 time or what ever admin define! this will be shown as notification on both user type....ones there is no agreement,then users can dispute eachother where admin can make decition. this is part 1 of project,ones success,we go for part 2....